The present invention discloses a well tool for use in a tubing string suspended in a well bore and more particularly involves a tubing testing tool for allowing a pressure-test to be performed on the tubing string to determine if the string has leaks therein.
Prior art tubing testers such as those disclosed in U.S. Pat. Nos. 3,329,007; 2,874,927; and 2,853,625 all generally comprise a spring-loaded flapper valve hingedly secured inside a housing and engageable with a valve seat therein. A sliding tubular mandrel is located inside the housing and arranged to abut the flapper valve and pivot it open in the housing, thereby communicating the housing bore with the bore of the tubular mandrel. One of the most critical areas of operation in the tubing tester primarily involves the mating surfaces of the valve seat and the flapper valve. The sealing surfaces between these two components are critical to the tool's operation and must be able to withstand the erosion and high pressures of fluids and fluid-solid slurries normally flowing through the tubing string.
The sealing ability of the flapper valve on its seat usually depends solely on a single circular sealing element made of an elastomeric substance and usually either bonded to either the flapper or the seat, or else trapped in a dovetail channel cut in the flapper or the valve seat.
Both of these prior art methods of providing seal elements suffer from serious disadvantages. The bonded seal is expensive to manufacture and is almost always unreliable because of the difficulty in obtaining good, tough 100% rubber-to-metal bonds. This seal method also suffers the disadvantage that when the seal must be replaced, the tool must be pulled out of the string, disassembled, and the flapper or valve seat returned to the bonding lab to have a new seal bonded thereon.
The alternate method is to machine a peripheral dovetail groove in the valve face or the valve seat face and force an elastomeric seal into the dovetail channel. The disadvantage of this method is that the seal must be small enough to allow entry into the groove without cutting or damaging the seal material. Under these circumstances, the seal then is highly susceptible to extrusion under pressure and being sucked out of place during high velocity fluid flow.
The present invention solves these two problems by providing a tubing tester construction which utilizes an easily replaceable seal element in a seal channel, which element does not have to be forced into the channel yet is held securely enough to prevent extrusion or velocity removal.